This website uses cookies to deliver some of our products and services as well as for analytics and to provide you a more personalized experience. Click here to learn more. By continuing to use this site, you agree to our use of cookies. We’ve also updated our Privacy Notice. Click here to see what’s new.

About Optics & Photonics TopicsOSA Publishing developed the Optics and Photonics Topics to help organize its diverse content more accurately by topic area. This topic browser contains over 2400 terms and is organized in a three-level hierarchy. Read more.

Topics can be refined further in the search results. The Topic facet will reveal the high-level topics associated with the articles returned in the search results.

Abstract

We investigate the effects of blood flow and extravascular tissue shearing on diffusing-wave spectroscopy (DWS) signals from deep tissue, using an ex vivo porcine kidney model perfused artificially at controlled arterial pressure and flow. Temporal autocorrelation functions g(1)(τ) of the multiply scattered light field show a decay which is described by diffusion for constant flow, with a diffusion coefficient scaling linearly with volume flow rate. Replacing blood by a non-scattering fluid reveals a flow-independent background dynamics of the extravascular tissue. For a sinusoidally driven perfusion, field autocorrelation functions g(1)(τ, t′) depend on the phase t′ within the pulsation cycle and are approximately described by diffusion. The effective diffusion coefficient Deff(t′) is modulated at the driving frequency in the presence of blood, showing coupling with flow rate; in the absence of blood, Deff(t′) is modulated at twice the driving frequency, indicating shearing of extravascular tissue as the origin of the DWS signal. For both constant and pulsatile flow the contribution of extravascular tissue shearing to the DWS signal is small.

Figures (9)

Fig. 1. Schematic experimental setup. The kidney, which is fixed in a rigid construction in order to minimize motion artefacts, is perfused by a computer-controlled perfusor consisting of a syringe driven by a linear motor at controlled velocity. The DWS sensor is placed on the Extremitas inferior and probes approximately the banana-shaped volume marked in pink. Injected fluid is drained through the vena renalis (not shown).

Fig. 2. Field autocorrelation functions g(1)(τ) as a function of lag time τ measured at the Extremitas inferior of the porcine kidney during constant perfusion with diluted blood for flow rates Q = 0.6mℓ/s (□), 1.2mℓ/s (◦), 1.8mℓ/s (△), 2.4mℓ/s (▽) and 3.1mℓ/s (◊). Source-receiver distance is ρ = 18mm. For better visibility of the flow dependence, data for lag times τ > 1ms are suppressed. Data are averages over 1908 autocorrelation functions each measured with an acquisition time of 26.2 ms, corresponding to a total experiment duration of 50s for each flow rate. Standard deviations of g(1)(τ) are smaller than 2×10−3.

Fig. 4. Particle diffusion coefficient D of the blood-perfused kidney as a function of volume flow rate Q. The full line is a linear least-squares fit to the data. Values for intercept and slope are (6.5±3.3)×10−14m2/s and (3.5±0.16)×10−13m2/mℓ, respectively. Error bars denote the standard deviation of the residuals of the fit to 〈Δφ2(τ)〉.

Fig. 6. (a) Arterial pressure pa(t′) and (b) flow rate Q(t′) as a function of phase t′ within the pulsation cycle. Circles: diluted blood; squares: saline solution. Data are averages over 31 and 16 measurements for diluted blood and for saline solutions, respectively, each with an integration time of 26.2 ms.

Fig. 7. Mean square phase fluctuation 〈Δφ2(τ, t′)〉 of the blood-perfused kidney as a function of lag time τ measured at different phases t′ in the pulsation cycle. Average flow rate Q = 1.2mℓ/s. The dashed line denotes, for comparison, the diffusive scaling 〈Δφ2(τ)〉 ~ τ observed for constant flow. Data are averages over 31 measurements each with an integration time of 26.2 ms.

Fig. 9. Real part of the spectrum of the effective diffusion coefficient Deff(t) for the kidney perfused with blood (red) and with saline buffer (black), as a function of frequency f. Note the strong peak at the pulsation frequency f0 = 1Hz and the marked second harmonic at 2Hz for the saline-perfused kidney indicating the contributions of extravascular tissue shearing.